Hydrogen (H2) is a useful energy source that has the potential to reduce the need for fossil fuels in the future, and may someday replace or serve as an important alternative to the current fossil-based transportation fuels [9-11]. Indeed, a great deal of effort has been put forth to develop H2-fueled motor vehicles in order to fulfill increasing energy demands for transportation. Also, H2 is present as a common reagent in industry and is used as an O2 scavenger in metallurgy, in hydrocracking for refined fuels, and in degradation of synthetic materials. However, utilizing H2 can be dangerous, as H2 has one of the lowest flash points (−253° C.) of any energy source, making it highly explosive in air above 4% H2 by volume [12]. Accordingly, one of the aims in fuel cell research is to safely store and release H2 in a controlled manner. For these reasons, it is important to develop simple, reliable, low-cost sensors for the detection of H2 over a range of concentrations.
Previously, arrays of palladium (Pd) mesowires have been synthesized by electrochemical deposition of Pd on the step-edges of highly-oriented pyrolytic graphite (HOPG), and the resistance change of these arrays in the presence of H2 has been examined after the arrays were transferred to a glass substrate and electrical contacts to the arrays were made [1,2]. In contrast to most Pd-based H2 sensing devices, which exhibit an increase in resistance in the presence of H2 due to the formation of the more resistive PdHx [3,4], the Pd mesowire arrays exhibited a significant decrease in resistance due to the formation of break junctions within the mesowires upon volume expansion of the PdHx [1,2]. These devices quantitatively detected H2 from 2 to 10% reversibly with 75 ms response times.
H2 sensing has also been performed with films of Pd nanoparticles prepared by physical deposition or chemical methods [5,6]. However, these Pd nanoparticle-based sensors also contain nanoscale gaps and operate on similar principles as the mesowire array[1,2]. Other nanoscale materials used for H2 sensing include carbon [7] and Pd nanotubes [8], which operate on different principles, but display low detection limits.
In any event, known methods and devices for detecting H2 are only capable of detecting H2 after assembling various sensors in a complicated multi-step process involving synthesis, assembly, and contact formation, or are only capable of assembling sensors that are unable to be constructed in a highly parallel fashion or with a near 100% success rate. Furthermore, none of the known methods and devices for detecting H2 have sufficiently provided a sensor whereby metal electrodeposition is used to make direct contract between a deposited metal and one or more electrodes, which is of great importance in eliminating the need for multi-step processes involving synthesis, assembly, and contact formation.